The present invention relates to an active matrix type liquid crystal display device and a method of producing the same. More particularly, the present invention relates to a surface planarization technique for a drive substrate of such a liquid crystal display device in wiring regions in which conductive lines are formed and regions between the conductive lines.
FIGS. 8A and 8B schematically show plan and sectional views, respectively, of a principal part of a drive substrate in a conventional active matrix type liquid crystal display device. FIGS. 9A and 9B schematically show plan and sectional views, respectively, of the principal part of the drive substrate in another conventional active matrix type liquid crystal display device. In these figures, same reference numbers are given to similar parts.
The structure of the conventional drive substrate shown in FIGS. 8A and 8B corresponds to that disclosed in JP-A-4-234820 (published in 1992). In these figures, reference numeral 12 designates a conductive line for wiring, reference numeral 13 designates a pixel electrode, reference numeral 14 designates an insulating film, and reference numeral 16 designates a substrate made up of an insulating film substrate 16a and under layers 16b formed on the insulating film substrate. This drive substrate is obtained by forming layers and patterns other than the conductive lines 12 and the pixel electrode 13 (i.e. the under layers 16b) on the insulating substrate 16a, then forming the insulating film 14, and then forming the pixel electrode 13 on the insulating film 14 as well as forming the lines 12. When the liquid crystal display device is a transmission type, it is required to use a transparent material for the insulating film 14 as well. Photosensitive transparent polyimide and the like are used, for example.
On the other hand, the structure of the conventional drive substrate shown in FIGS. 9A and 9B is formed according to the technique disclosed in JP-A-4-338718 (published in 1992). According to this prior art, in order to flush top surfaces of the lines 12 and the pixel electrode 13, namely, to make the levels of these parts identical, a transparent insulating film 14 is placed under the pixel electrode 13 to form a convex part.
Alternatively, the lines are etched beforehand to form concave parts. Next, the lines 12 are coated with an insulating material 15, whereby the level difference between the lines 12 and the transparent pixel electrode 13 is canceled. As the insulating material 15, for example, polyimide is used.
In the above two prior arts, the insulating film 14 is not associated with the lines 12 (FIGS. 8A and 8B) or the lines 12 coated with the insulating material 15 (FIGS. 9A and 9B) to form a surface that is continuous at the same level. Therefore, a region in which the pixel electrode 13 is formable is limited to an upper surface of the insulating film 14. In order to explain a reason why the region in which the pixel electrode 13 is formable is limited to an upper surface of the insulating film 14, FIGS. 10 and 11 show cases where the structures shown in FIGS. 8A and 8B and FIGS. 9A and 9B have been modified such that pixel electrode-forming region is expanded beyond the insulating film 14 onto the lines 12. In FIG. 10, the lines 12 are directly connected to the pixel electrodes 13, and thus, disadvantageously, the pixels are always electrically connected to the lines 12. Further, in both of the cases of FIGS. 10 and 11, uneven portions (concave portions) arise in the pixel electrodes 13 due to gaps between the lines and the insulating film. Therefore, in a rubbing step conducting an orientation treatment of the liquid crystal, the orientation treatment cannot be performed uniformly due to barriers attributed to the unevenness of the pixel electrodes, resulting in a deterioration of the degree of orientation at the concave portions, namely in the gaps. Because of the reason mentioned above, the pixel electrode 13 cannot be formed on regions other than the insulating film 14 in these prior arts. This leads to a reduction in the numerical aperture, which is inconvenient for the liquid crystal display device.
An object of the present invention is to provide an active matrix type liquid crystal display device in which a plurality of scanning lines and a plurality of signal lines are arrayed on an insulating substrate in such directions that the scanning lines intersect the signal lines, and in which pixel electrodes are flatly formed even on the scanning lines and/or the signal lines so that the numerical aperture can be improved, and also to provide a method of producing such a device.
In order to achieve the above object, there is provided a liquid crystal display device according to an aspect of the present invention in which a plurality of scanning lines and a plurality of signal lines are arrayed on an insulating substrate in such directions that the scanning lines and the signal lines intersect each other, comprising:
insulating film patterns each formed between the adjacent scanning lines and/or between the adjacent signal lines;
an upper insulating film formed on the insulating film patterns and the lines between which the respective insulating film patterns are formed, and in spaces between the insulating film patterns and the lines, said upper insulating film having a continuous top surface at a same or approximately same level; and
pixel electrodes formed on the upper insulating film.
In this liquid crystal display device, since the upper insulating film, which is formed on the lines and between the lines, has a continuous top surface at the same or approximately same level, it is possible that the whole surface of the pixel electrode also has a same or approximately same level. That is, in all the regions on the lines and between the lines, a structure planarized at an identical level is obtained. Accordingly, it becomes possible to conduct uniform orientation treatment. Also, since the upper insulating film, which is formed on the lines and between the lines, has a continuous top surface at the same or substantially same level, it becomes possible to expand the pixel electrode-forming region towards above the lines without limiting it to between the lines. Therefore, the numerical aperture can be improved.
Further, according to another aspect of the invention, there is provided a method of producing a liquid crystal display device in which a plurality of scanning lines and a plurality of signal lines are arrayed on an insulating substrate in such directions that the scanning lines and the signal lines intersect each other, comprising:
forming an insulating film pattern between the adjacent scanning lines and/or the adjacent signal lines; and
forming an upper insulating film on the insulating film patterns and the lines and in spaces between the insulating film patterns and the lines in such a manner that the upper insulating film has a continuous top surface at a same or approximately same level.
According to this method, the upper insulating film is formed on the lines and between the lines so as to have a continuous top surface at the same or approximately same level. Therefore, it becomes possible to expand the pixel electrode-forming region towards above the lines without limiting it to between the lines, and thus an improvement in the numerical aperture can be attained. Also, if the pixel electrode is formed on the upper insulating film, it is possible that the whole surface of the pixel electrode also has the same or approximately same level. Therefore, a structure planarized at an identical or approximately identical level in all the regions on the lines and between the lines is obtained. Accordingly it becomes possible to conduct uniform orientation treatment.
In order to ensure that the upper insulating film fills spaces between the insulating film patterns and the lines adjacent to the insulating film patterns, the upper insulating film may be preferably formed so as to have a film thickness that is at least xc2xd of the space between the insulating film patterns and the lines adjacent to the insulating film patterns. The upper insulating film formed to such a film thickness may be used as is, or it may be thinned by an etch-back method. By etching back the upper insulating film, the upper insulating film having a desired film thickness is obtained. Furthermore, the flatness is more improved.
When the present invention is applied to a transmission type liquid crystal display device, the upper insulating film pattern may be formed from a transparent film having a refractive index of 1.4-1.95.
Further, if a lower insulating film, which is made of a material different from materials of the insulating film patterns and the upper insulating film, is formed before forming the upper insulating film patterns, the lower insulating film serves as an etching stopper in the etching process for forming the insulating film patterns and in the etching process for the upper insulating film.
Other objects, features and advantages of the present invention will be obvious from the following description.